SaveAs Dialogue box is not working on button click in servlet

Hii Sir, i added response.setHeader into my servlet code to export the data into excel file but this is not working on button click ...plz give me the write code. Thank you Sir.

response.setHeader("Content-Type", "application/vnd.ms-excel"); response.setHeader("Content-Disposition","attachment; filename=excel.xls");

String datum1 = request.getParameter("fromdate");
String datum2 = request.getParameter("todate");
SimpleDateFormat sdfSource = new SimpleDateFormat("dd-MM-yyyy");
Date date = sdfSource.parse(datum1);
Date date2 = sdfSource.parse(datum2);
SimpleDateFormat sdfDestination = new SimpleDateFormat("yyyy-MM-dd");
datum1 = sdfDestination.format(date);
System.out.println(datum1);
datum2 = sdfDestination.format(date2);
System.out.println(datum2);


HSSFWorkbook hwb = new HSSFWorkbook();
HSSFSheet sheet = hwb.createSheet("CallBillingSystem");

HSSFRow rowhead = sheet.createRow((short) 0);
rowhead.createCell((short) 0).setCellValue("calldate");
rowhead.createCell((short) 1).setCellValue("src");
rowhead.createCell((short) 2).setCellValue("dst");
rowhead.createCell((short) 3).setCellValue("dstchannel");
rowhead.createCell((short) 4).setCellValue("lastapp");
rowhead.createCell((short) 5).setCellValue("duration");
rowhead.createCell((short) 6).setCellValue("disposition");
rowhead.createCell((short) 7).setCellValue("amaflags");
rowhead.createCell((short) 8).setCellValue("cdrcost");


String strQuery = "";
ResultSet rs = null;

conexion conexiondb = new conexion();
conexiondb.Conectar();

strQuery = "SELECT * FROM cdrcost where date(calldate) between '" + datum1 + "' and '" + datum2 + "'";

 //strQuery = "SELECT * FROM cdrcost where date(calldate) between '2011-09-01' and '2012-01-01'";

rs = conexiondb.Consulta(strQuery);
int i = 1;
while (rs.next()) {
    HSSFRow row = sheet.createRow((short) i);
    row.createCell((short) 0).setCellValue(rs.getString("calldate"));
    row.createCell((short) 1).setCellValue(rs.getString("src"));
    row.createCell((short) 2).setCellValue(rs.getString("dst"));
    row.createCell((short) 3).setCellValue(rs.getString("dstchannel"));
    row.createCell((short) 4).setCellValue(rs.getString("lastapp"));
    row.createCell((short) 5).setCellValue(rs.getString("duration"));
    row.createCell((short) 6).setCellValue(rs.getString("disposition"));
    row.createCell((short) 7).setCellValue(rs.getString("amaflags"));
    row.createCell((short) 8).setCellValue(rs.getString("cdrcost"));
    i++;
}
FileOutputStream fileOut = new FileOutputStream(filename);
hwb.write(fileOut);     
hwb.write(response.getOutputStream());
System.out.println("Your excel file has been generated!");
FileOut.close();

} catch (Exception ex) { System.out.println(ex);

}

}